Are there any textual CAPTCHA challenges which can fool AI, but not human?
A method that could possibly work is utilising optical illusions such as one where two lines down a hallway are identical but one seems longer to the human eye, then they could be prompted with a multiple choice question as to the state of the line, which to our eyes looks longer, but to a computer, is still the same length of line. Of course, there is always the issue of people with eye based disabilities not being able to complete them, but different illusions could be used to accommodate that.

Example